1. Field of the Invention
The present invention relates to a two-legged walking robot, and more particularly, to a two-legged walking robot having improved joint parts.
2. Description of the Related Art
Generally, a two-legged walking robot includes a skeletal frame to provide a pair of legs like human legs, a joint part pivotably provided between bones of the skeletal frame, and an actuator connected to bones to rotate the bones at the joint part.
The skeletal frame includes a foot member to step on a ground like a human foot, a calf member provided above the foot member, a femoral member provided above the calf member, and a hip member provided above the femoral member like a human hip.
The joint part includes an ankle joint provided between the foot member and the calf member, a knee joint provided between the calf member and the femoral member, and a hip joint provided between the femoral member and the hip member.
In the two-legged walking robot, the actuator connecting the foot member with the calf member rotates the foot member relative to the calf member about the ankle joint. The actuator connecting the calf member with the femoral member rotates the calf member relative to the femoral member about the knee joint, and the actuator connecting the femoral member with the hip member rotates the femoral member relative to the hip member about the hip joint.
As shown in FIG. 1, a conventional two-legged walking robot includes a foot member 11, a calf member 12, a femoral member 13, and a hip member 14, which are respectively connected by joint parts 15, 16, 17 and assembled into a leg assembly to support a robot body. Hereinafter, to avoid repetitive description, a mechanism of one leg assembly will be described because the left leg assembly and the right leg assembly are of the same configuration. The joint parts include an ankle joint 15, a knee joint 16 and a hip joint 17.
In the leg assembly, each member is connected to an actuator to provide a four-bar linkage (e.g., quadric crank mechanism). The actuator makes a linear-sliding motion with a ball screw. The linear-sliding motion changes a rotation angle between links, thereby bending or stretching the leg assemblies of the walking robot.
More particularly, to cause the bending and stretching operation in the ankle joint 15, a middle part of a first actuator 30a is pivotably connected to a middle part of the calf member 12 by a first link 21, and a slider 35a of the first actuator 30a is pivotably connected to a middle part of the foot member 11.
To cause the bending and stretching operation in the knee joint 16, a lower part of a second actuator 30b is pivotably connected to an upper part of the foot member 11 by a second link 22, and a middle part of the second actuator 30b is pivotably connected to a middle part of the femoral member 13 by a third link 23.
To cause the bending and stretching operation in the hip joint 17, a lower part of a third actuator 30c is pivotably connected to an upper part of the femoral member 13 by a fourth link 24, and a middle part of the third actuator 30c is pivotably connected to the hip member 14 by a fifth link 25.
According to the above, the bending and stretching operations in the joints 15, 16, 17 are performed by the actuators 30a, 30b, 30c, respectively.
The actuator 30a, 30b, 30c includes a motor 31a, 31b, 31c to rotate the ball screw 33a, 33b, 33c, an encoder 32a, 32b, 32c to determine a rotation state of the motor 31a, 31b, 31c, a guide rail 34a, 34b, 34c disposed parallel with the ball screw 33a, 33b, 33c, and the slider 35a, 35b, 35c coupled to the guide rail 34a, 34b, 34c and linearly movable by rotation of the ball screw 33a, 33b, 33c. 
The slider 35a, 35b, 35c has a first part slidingly coupled to the guide rail 34a, 34b, 34c, and a second part having a female screw engaged with the ball screw 33a, 33b, 33c to be operated by the rotation of the ball screw 33a, 33b, 33c. The encoder 32a, 32b, 32c is attached to a rear of the motor 31a, 31b, 31c and employed to servo-control the motor 31a, 31b, 31c. 
According to the above configuration, a walking operation of the conventional two-legged walking robot is achieved by the actuators 30a, 30b, 30c connected to the joints 15, 16, 17.
However, in the conventional two-legged walking robot, the joints 15, 16, 17 allow the leg assemblies to be bent and stretched in only forward and backward directions, so that the leg assemblies have a low degree of freedom as compared to the human legs.